Focussing mask for cathode ray tube



Dec. 12, 1961 R. D. EATON 3,

FOCUSSING MASK FOR CATHODE RAY TUBE Filed March 25, 1953DDIJUUUEIEIDEIDDUUDDDUEIIJEIDDD F ig.

INVENTOR. ROLAND D. EATON p wfifiw I 11 12 A T TORNEiKS 3,013,178FOCUSSING MASK FGR CATHODE RAY TUBE Roland D. Eaton, Radburn, Nl,assignor to Fairchild Camera and instrument Corporation, a corporationof Delaware Filed Mar. 23, 1953, Ser. No. 343,988 Claims. (Cl. 315-13)This invention relates to color television and more particularly to adual-purpose mask for a color television tube.

In reproducing color television pictures prior art practice has been toprovide a fluorescent screen with a pattern of dots of fluorescentmaterials laid down in a geometrical pattern, each material fluorescingin a different color when excited by an electron beam. Three sources ofelectron beams are provided, and by suitable masking means each beam iscaused to impinge on one and only one type of fluorescent material. Alldots of the same color emitting property are excited by the beam fromthe same source.

An object of this invention is to provide a perforated mask for aplurality of electron beams from several electron guns impinging upon afluorescent screen having a definite dot pattern, each dot offluorescent material emitting light of a different color when excited byan electron beam, and to increase efficiency by providing holes in themask considerably larger than the color dots on the screen.

Another object of this invention is to provide means in combination withthe aforesaid perforated mask to focus these beams onto the fluorescentdots.

These and other objects of the invention will become apparent from astudy of the following specification in connection with the attacheddrawing in which,

FIGURE 1 is a sectional view, greatly enlarged, through a portion of themask showing the paths of several beams from the electron guns to thefluorescent screen; and

FIGURE 2 is a somewhat diagrammatic view of the color picture tube inwhich the invention is practiced, parts being broken away to show theinternal construction.

The invention contemplates the utilization of a masking plate comprisinga sheet of glass 11, preferably of the type known as photo-etched glass,manufactured by the Corning Glass Co., which has been exposed to lightthrough an opaque mask in which a myriad of small holes in a regulargeometric pattern have been etched. The action of light on thisphotosensitive glass is to change its character so that it may be etchedaway from the rest of the glass by suitable processes.

The etched glass plate 11 is sprayed or coated on each side with a thinlayer 12 and 12a of a barrier coat such as lacquer which covers theholes as well as the glass as shown at A in FIGURE 1. A layer ofaluminum 13 and 13a is then evaporated onto the barrier layer on eachside of the mask. Thereafter the plate is baked at a temperature ofapproximately 380 C. to burn out the barrier layer. The aluminumcovering of the openings in the plate 11 is then removed. Air may beblown through the holes which blows out the thin unsupported aluminum asshown at B and the plate is then ready for use.

The plate 11 is mounted in the cathode ray tube 14 at a fixed distancefrom the color, dot screen 15 (as shown in 'FIGURE 2) in accordance withknown principles. Leads from each of the deposited aluminum surfaces arebrought out to contacts 16 and 17 on the outer surface of the glassenvelope. Screen 15 has an aluminized surface and a lead from thissurface is brought out to a contact 18 on the envelope.

Suitable sources of potential 19, 20 and 21 are connected to the tubeelements and to the aluminum layers to provide increasing potential fromthe electron gun structures, shown diagrammatically at 2-2, through themask 11 to the screen 15. A difference of potential is applied betweenthe aluminum layers 13 and 13a of the mask. This potential differenceprovides an electron lens or a focussing action which takes place at themask to focus the beam on the individual dots of the color dot screen.

Referring back to FIGURE 1, the electron beams from the electron guns,shown diagrammatically and identified as sources 23, 24 and 25 areprojected through the apertures in the mask 11 and focussed on the colordots 26, 27 and 28 respectively of screen 15. While there is initialfocussing at the electron gun sources of the electron beam, postfocussing takes place at the mask 11 thereby to insure that the beam issharply focussed on the dots of the screen 15.

This post focussing at the mask makes possible greater electrontransmission efficiency than heretofore achieved. The individualperforations in the mask may be of a size greater than the individualcolor dots, the focussing action of the mask concentrating theelectronbeam andreducing its size to the size of the dots. This action permitspassage of more of the beam than that of the prior art masks thusproviding greater screen light output. Also it effectively overcomes theheating effect of the electrons striking the mask which causes warping,a difficulty experienced with the prior art masks. Prior art maskspermit about 25 to 30% electron transmission. The mask structure inaccordance with this invention allows up to 70% electron transmission.

While I have described and illustrated one specific embodiment of theinvention, other embodiments are apparent as defined by the followingclaims.

What is claimed is:

1. In a cathode-ray tube having a fluorescent screen in the form of aplurality of dots of material fluorescing when excited by an electronbeam and a plurality of electron guns for generating and directingelectron beams onto said screen, the improvement comprising: aperforated mask of electrical insulating material'positioned betweensaid fluorescent screen and said electron guns, said perforated maskbeing provided with an electrical conducting layer on each surfacethereof, each said layer being perforated corresponding to theperforations in said mask.

2. The apparatus of claim 1 including a source having a plurality ofelectrical potentials, each said conducting layer on said mask beingconnected to said source at different potentials whereby a potentialdifference may exist between said layers.

3. The apparatus of claim 1, in which said perforations are larger thansaid dots thereby to provide a high electron transmission efficiency.

4. The apparatus of claim 1 including an electrical conducting layer onsaid screen and a source of a plurality of potentials, said conductinglayer on said screen being connected to said source at one potential andsaid layers on said mask being connected to said source at otherpotentials whereby potential differences exist between said layers onsaid mask and said layer on said screen.

5. In a cathode ray tube having a fluorescent screen in the form of aplurality of dots of material fluorescing when excited by an electronbeam, a plurality of sources of electron beams, said beams beingdirected at said screen, the improvement comprising: a perforated masklocated between said screen and said sources to shade said screen sothat only beams coming from one of said sources can strike certain ofsaid dots and beams from others of said sources can strike others ofsaid dots,

said perforated mask comprising a sandwich consisting of an electricalinsulating material between two electrical conducting layers, saidsandwich forming a unitary structure and each perforation in said maskextending entirely through said sandwichyeach of said perforations beinglarger in cross-sectional area than the dots most closely adjacentthereto, a conductive layer on said screen, and a source having aplurality of potentials, one of said potentials being connected to saidconducting layer on said screen, a second of said potentials beingconnected to one conducting layer on said sandwich and a third potentialbeing connected to the other conducting layer on said sandwich, themagnitude relationship between said three potentials being such as toconstrict the electron beams passing through said perforations to thearea of said dots.

References Cited in the file of this patent UNITED STATES PATENTSOkolicsanyi June 23, Sabbah Sept. 19, Schlesinger n- Dec. 27, MortonMar. 7, Blumlein July 4, Hinsch Dec. 31, Bondley Jan. 25, Salisbury July18, Jenny Ian. 8, Faulkner et al Sept. 16, Rajchman Nov. '25, EpsteinNov. 10, Law Dec. 22,

